Methods of forming a metal alloy

ABSTRACT

A method of forming a metal alloy. The method comprises forming a metal oxide precursor and conducting cathodic polarization of the metal oxide precursor in a molten salt electrolyte to form a metal alloy. In an additional method, a metal oxide precursor is formed. The metal oxide precursor is reduced to a metal in an electrochemical cell that comprises a working electrode, a counter electrode, and an electrolyte. The metal is reacted with a metal of the working electrode to form a metal alloy. In another method, a metal oxide precursor is formed on a base material. The base material is introduced into a molten salt electrolyte of an electrochemical cell and the metal oxide precursor is reduced to a metal in the electrochemical cell. The metal is reacted with the base material to form a metal alloy on the base material.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application Ser. No. 62/706,337, filed Aug. 11, 2020, the disclosure of which is hereby incorporated herein in its entirety by this reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under Contract Number DE-AC07-05ID14517 awarded by the United States Department of Energy. The government has certain rights in the invention.

TECHNICAL FIELD

The disclosure, in various embodiments, relates to methods of forming a metal (e.g., a metal alloy). Specifically, the disclosure, in various embodiments, relates to methods of forming a tantalum alloy.

BACKGROUND

Refractory metals, refractory metal alloys, transition metals, and transition metal alloys have been used as structural and functional materials in a variety of industries, such as in the biomedical industry, the corrosion industry, the aerospace industry, the nuclear industry, the lighting industry, or the automotive industry. Different properties of these materials enable their use in such disparate industries. For instance, compatibility of refractory metals and refractory metal alloys inside the human body enables their use in medical devices. Tantalum and tantalum-titanium alloys are bio-compatible and used in medical devices, such as orthopedic medical devices. The biocompatibility of tantalum and tantalum-titanium alloys includes corrosion-resistance, adequate mechanical strength, chemical inertness towards body fluid, low density etc. Other tantalum alloys, such as tantalum-hafnium alloys, exhibit different properties, such as good strength, corrosion resistance properties at very high temperatures (>1500° C.), and good room-temperature/sub-zero temperature ductility.

Powder metallurgical (PM) processes and melting processes are conventionally used to form tantalum alloys. However, since these materials are sensitive to air and/or oxidation, specialized techniques (vacuum-arc melting, electron beam melting, plasma melting, vacuum induction melting) are used to fabricate the tantalum alloys, which are subsequently formed into desired shapes by metallurgical processes, such as sintering, pressure bonding, injection molding, casting, extruding, calendaring, etc. Therefore, many of these processes include multiple steps to form the metal alloy.

BRIEF SUMMARY

A method of forming a metal alloy is disclosed. The method comprises forming a metal oxide precursor on a substrate and conducting cathodic polarization of the metal oxide precursor in a molten salt electrolyte to form a metal alloy on the substrate.

Another method of forming a metal alloy is disclosed. The method comprises forming a metal oxide precursor. The metal oxide precursor is reduced to a metal in an electrochemical cell that comprises a working electrode, a counter electrode, and an electrolyte. The metal of the metal oxide precursor is reacted with a metal of the working electrode to form a metal alloy.

Yet another method of forming a metal alloy is disclosed. The method comprises forming a metal oxide precursor on a base material. The base material is introduced into a molten salt electrolyte of an electrochemical cell. The metal oxide precursor is reduced to a metal in the electrochemical cell. The metal of the metal oxide precursor is reacted with the base material to form a metal alloy on the base material.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a simplified schematic illustrating an electrochemical cell configured for electrochemically reducing a metal oxide precursor, in accordance with embodiments of the disclosure;

FIG. 2 is a photograph of sintered tantalum oxide and titanium oxide pellets, with an air-sintered pellet shown on the left and a sintered-in-a-reducing-atmosphere pellet shown on the right;

FIG. 3 is a photograph of a tantalum-titanium alloy in powder form, prepared from the sintered-in-a-reducing-atmosphere pellet of FIG. 2;

FIG. 4 is a photograph of sintered tantalum oxide and hafnium oxide pellets, with an air-sintered pellet shown on the left and the sintered-in-a-reducing-atmosphere pellet shown on the right;

FIG. 5 is a photograph of sintered tantalum oxide and tungsten oxide pellets, with an air-sintered pellet shown on the left and the sintered-in-a-reducing-atmosphere pellet shown on the right;

FIG. 6 is a photograph of a tantalum-tungsten alloy on a metal wire; and

FIG. 7 is a photograph of a diffused tantalum interlayer between a tantalum layer and a base material.

DETAILED DESCRIPTION

Methods of forming a metal (e.g., a metal alloy) are disclosed. The metal alloy may be a transition metal alloy or a refractory metal alloy. The metal alloy may be formed by cathodic polarization of a metal oxide precursor in an electrolyte (e.g., a molten salt electrolyte) against a counter electrode (e.g., an anode material). During the cathodic polarization, the metal alloy may be formed in situ by removing oxygen from the metal oxide precursor. The resulting metal alloy may include a low oxygen content than metal alloys formed by conventional techniques. The methods may be used to form a coating of the metal alloy on a substrate or to form a large amount of the metal alloy (e.g., a bulk metal alloy). The methods of forming the metal alloy according to embodiments of the disclosure may utilize molten salt electrometallurgical processes. The metal oxide precursor may include a single metal oxide (e.g., a unitary metal oxide) or may include multiple metal oxides (e.g., a mixed metal oxide, a binary metal oxide, a ternary metal oxide, a quaternary metal oxide) to form the metal alloy (e.g., a binary metal alloy, a ternary metal alloy, a quaternary metal alloy). The methods of forming the metal alloy according to embodiments of the disclosure are more cost effective, have a reduced carbon footprint, and are less harmful to the environment than conventional methods of forming the metal alloy, such as powder metallurgical (PM) processes, conventional melt deposition processes, or laser melt processes. In addition, the polarization process enables the metal alloy to be formed at a lower temperature than conventional processes. The polarization process also enables the metal alloy to be formed quickly and more efficiently than conventional processes by reducing the amount of time for chemical reduction of the metal oxide to a metal. The metal alloy is formed as the coating or the bulk material by utilizing a modified electrochemical process.

A composition of the metal alloy may be tailored by adjusting process parameters, which increases versatility of the methods according to embodiments of the disclosure. An article containing the metal alloy may exhibit improved temperature resistance, corrosion resistance, and/or oxidation resistance properties compared to articles containing the metal alloy formed by conventional techniques. Articles including the metal alloy may be used in a variety of industries, such as in the biomedical industry (orthopedic applications), the corrosion industry, the aerospace industry, nuclear, lighting, or the automotive industry. The metal alloy may, for example, be used in valves, tube fittings, cam and groove couplings, pump impellers, flanges and pipe fittings, agitators and stirrers, heat exchangers, thermophotovoltaics (TPVs), solar TPV, solar-thermal energy conversion systems, joint implants, fasteners, spinal and dental implants, and stents.

As used herein, the term “transition metal” means and includes scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, yttrium, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, cadmium, lanthanum, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, or gold.

As used herein, the term “refractory metal” means and includes titanium, vanadium, chromium, manganese, zirconium, niobium, molybdenum, ruthenium, rhodium, hafnium, tantalum, tungsten, rhenium, osmium, or iridium.

The method according to embodiments of the disclosure is used to form the metal alloy, such as a transition metal alloy or a refractory metal alloy. By way of example only, the metal alloy may be a tantalum alloy, such as a tantalum-titanium alloy, a tantalum-hafnium alloy, a tantalum-tungsten alloy, or a tantalum-molybdenum alloy. However, other tantalum alloys may be prepared by similar methods. The metal alloy may be fabricated from the metal oxide precursor or the mixed metal oxide precursor (e.g., the binary metal oxide, the ternary metal oxide) following reduction of the metal oxide precursor or the mixed metal oxide precursor. The metal oxide precursor may be prepared by air sintering or by heating in a reductive environment. The metal oxide precursor may be an insulating metal oxide. The metal oxide precursor or the mixed metal oxide precursor may be maintained in intimate contact with (e.g., direct contact with) a current collector (e.g., a metal wire) during the polarization in an electrolyte. The metal wire may be a titanium wire, a nickel wire, a tantalum wire, a tungsten wire, a hafnium wire, an Inconel wire, or a molybdenum wire. Electroreduction of the metal oxide occurs in an electrochemical cell, forming the metal from the metal oxide precursor. The metal oxide precursor or the mixed metal oxide precursor is reduced (e.g., chemically reduced) in the electrochemical cell to the metal or metals, respectively, and reacted with the current collector to form the metal alloy. The metal or metals of the metal oxide precursor may be reacted with the metal of the current collector. The metal wire (e.g., the current collector) may be reacted with the reduced metal or reduced metals, such as at a cathode, to form the metal alloy in situ. A composition of the metal alloy may be tailored by adjusting conditions of the polarization.

The metal oxide precursor may be an oxide precursor of a first metal, such as tantalum oxide (Ta₂O₅). The metal oxide precursor may be prepared by air-sintering or heating under reducing gas-flow conditions, such as pure hydrogen gas (H₂) or a combination of argon/hydrogen gas (H₂). The metal oxide precursor of the first metal may be sintered in air or under a reducing atmosphere and then threaded into a wire of a second metal, which is immersed in an electrolyte and polarized (e.g., exposed to polarization conditions). The second metal may be titanium, nickel, tantalum, tungsten, hafnium, or molybdenum. The first metal may be a metallic wire wrapped around the metal oxide or the metal oxide may be threaded into the metallic wire during the reduction process. Kinetics of the metal oxide reduction may be faster when the metal oxide precursor is formed under the reducing gas-flow conditions. Forming the metal oxide precursor in a reducing atmosphere (under continuous dry hydrogen flow) may result in substantially complete reduction of the metal oxide to the metal compared to forming the metal oxide precursor in the air-sintered environment. Therefore, a metal alloy formed from the metal oxide precursor prepared under the reducing gas-flow conditions may include a lower residual oxygen content than a metal alloy formed from the air-sintered metal oxide precursor. The metal alloy formed under the reducing gas-flow conditions may exhibit about 50% less oxygen than the metal alloy formed from the air-sintered metal oxide precursor. The metal oxide formed under the reducing atmosphere may also exhibit a higher quality, producing a higher quality alloy. The metal alloy may be prepared under the reducing gas-flow conditions prior to treatment in an electrochemical cell (i.e., prior to the electrochemical polarization). If the first metal includes tantalum and the second metal includes titanium, the tantalum-titanium alloys according to embodiments of the disclosure may exhibit improved biomechanical properties compared to either pure tantalum or several orthopedic grade titanium alloys.

The reduction of the metal oxide precursor and the formation of the metal alloy may be conducted in an electrochemical cell 160 that includes a crucible 162, a working electrode 166 (also referred to as a cathode), a counter electrode 168 (also referred to as an anode), an electrolyte 164 (e.g., a molten salt electrolyte 164), and a reference electrode 170, as shown in FIG. 1. In some embodiments, the cathode functions as the material (e.g., substrate, wire) to be plated with the metal alloy. The electrochemical cell 160 may be housed in a glove box, such as an argon atmosphere glove box, to reduce exposure of sensitive components to moisture and/or oxygen. The crucible 162 is configured to contain the molten salt electrolyte 164. Each of the working electrode 166, the counter electrode 168, and the reference electrode 170 is at least partially disposed in the molten salt electrolyte 164 and in contact with the molten salt electrolyte 164. The molten salt electrolyte 164 may function as a solvent as well as to remove oxygen from the metal oxide precursor during formation of the metal alloy. When an electrical potential is applied between the working electrode 166 and the counter electrode 168, the metal oxide of the metal oxide precursor may be reduced in the electrochemical cell 160.

The crucible 162 may be formed of and include a ceramic material (e.g., alumina, magnesia (MgO), boron nitride (BN)), graphite, or a metallic material (e.g., nickel, stainless steel, molybdenum, or an alloy of nickel including chromium and iron, such as INCONEL®, commercially available from Special Metals Corporation of New Hartford, N.Y.

The counter electrode 168 may be formed of and include one or more of graphite (e.g., high density graphite), a platinum group metal (e.g., platinum, osmium, iridium, ruthenium, rhodium, and palladium), an oxygen evolving electrode, or another material. By way of example only, the counter electrode 168 may be formed of and include osmium, ruthenium, rhodium, iridium, palladium, platinum, silver, gold, lithium iridate (Li₂IrO₃), lithium ruthenate (Li₂RuO₃), a lithium rhodate (LiRhO₂, LiRhO₃), a lithium tin oxygen compound (e.g., Li₂SnO₃), a lithium manganese oxygen compound (e.g., Li₂MnO₃), calcium ruthenate (CaRuO₃), strontium ruthenium ternary compounds (e.g., SrRuO₃, Sr₂RuO₃, Sr₂RuO₄), CaIrO₃, strontium iridate (e.g., SrIrO₃, SrIrO₄, Sr₂IrO₄), calcium platinate (CaPtO₃), strontium platinate (SrPtO₄), magnesium ruthenate (MgRuO₄), magnesium iridate (MgIrO₄), sodium ruthenate (Na₂RuO₄), sodium iridate (Na₂IrO₃), potassium iridate (K₂IrO₃), or potassium ruthenate (K₂RuO₄). In some embodiments, the counter electrode 168 comprises graphite. In other embodiments, the counter electrode 168 comprises one or more platinum group metals. If the counter electrode 168 comprises iridium or ruthenium, the methods according to embodiments of the disclosure may be substantially non-polluting. In some embodiments, the counter electrode 168 comprises one or more platinum group metals (e.g., ruthenium, rhodium, palladium, osmium, iridium, and platinum), and one or more transition metals.

The reference electrode 170 may comprise any suitable materials and is configured for monitoring a potential in the electrochemical cell 160. In some embodiments, the reference electrode 170 comprises glassy carbon.

The molten salt electrolyte 164 may be disposed within the crucible 162 and may include a material formulated and configured to facilitate reduction of the metal oxide of the metal oxide precursor. The molten salt electrolyte 164 may comprise, for example, a molten salt, such as an alkali halide salt, an alkaline earth metal halide salt, an alkali oxide, an alkaline earth metal oxide, or combinations thereof. The molten salt electrolyte 164 may be formed of and include lithium chloride (LiCl), lithium oxide (Li₂O), sodium chloride (NaCl), calcium chloride (CaCl₂)), calcium oxide (CaO), lithium bromide (LiBr), potassium bromide (KBr), cesium bromide (CsBr), calcium bromide (CaBr₂), potassium chloride (KCl), potassium bromide (KBr), strontium chloride (SrCl₂), strontium bromide (SrBr₂), or a combination thereof. The electrolyte may be a CaCl₂) electrolyte, such as a CaCl₂/CaO electrolyte. In some such embodiments, the calcium oxide constitutes between about 0.25 weight percent (wt. %) and about 5.0 wt. % of the molten salt electrolyte 164, such as between about 0.5 wt. % and about 2.0 wt. %, or between about 1.5 wt. % and about 2.5 wt. % of the molten salt electrolyte 164. The calcium chloride may constitute a remainder of the molten salt electrolyte 164. In some embodiments, the calcium oxide constitutes about 1.0 wt. % of the molten salt electrolyte 164.

The molten salt electrolyte 164 may be formulated and configured to exhibit a melting temperature within a range of from about 550° C. to about 950° C., such as from about 550° C. to about 650° C., from about 650° C. to about 750° C., from about 750° C. to about 850° C., or from about 850° C. to about 950° C. The molten salt electrolyte 164 may be maintained at a temperature such that the molten salt electrolyte 164 is, and remains, in a molten state. In other words, the temperature of the molten salt electrolyte 164 may be maintained at or above a melting temperature of the molten salt electrolyte 164.

The current collector of the working electrode 166 may comprise, for example, a wire. The current collector of the working electrode 166 may be coupled to a basket 172 configured to contain metal oxide precursor 174. In some embodiments, the basket 172 comprises a wire basket and comprises the same material composition as the current collector of the working electrode 166.

The metal oxide precursor 174 may be coupled to (e.g., directly contact) at least one of the current collector of the working electrode 166 and the basket 172. In some embodiments, the metal oxide precursor 174 includes a portion sized and shaped to receive a portion of the current collector of the working electrode 166. By way of non-limiting example, a portion of the current collector of the working electrode 166 may be fed through a portion of the metal oxide precursor 174. As one example, the metal oxide precursor 174 may include an aperture configured to receive the portion of the current collector of the working electrode 166.

The counter electrode material may also be a non-carbonaceous electrode, as disclosed in application Ser. No. 15/886,041 filed Feb. 1, 2018, now U.S. Pat. No. 10,872,705, issued Dec. 22, 2020, titled “ELECTROCHEMICAL CELLS FOR DIRECT OXIDE REDUCTION, AND RELATED METHODS,” application Ser. No. 16/388,272, filed Apr. 18, 2019, and Application Ser. No. 62/661,881, filed Apr. 24, 2018, titled “METHODS OF FORMING ALLOYS BY REDUCING METAL OXIDES,” and Application Ser. No. 62/883,853, filed Aug. 7, 2019, titled “BINARY ALLOYS AS POTENTIAL ANODE MATERIALS,” and application Ser. No. 17/444,482, filed Aug. 5, 2021, titled “ANODES COMPRISING TRANSITION METAL AND PLATINUM GROUP METAL AS ALLOYS, AND RELATED METHODS AND SYSTEMS,” the entire disclosure of each of which is hereby incorporated herein in its entirety by this reference.

In use and operation, a voltage may be applied between the working electrode 166 and the counter electrode 168 to facilitate reduction of the metal oxide precursor 174 in the molten salt electrolyte 164. The voltage between the working electrode 166 and the counter electrode 168 may be within a range of from about 2.5 V to about 3.1 V, such as from about 2.5 V to about 2.7 V, from about 2.7 V to about 2.9 V, or from about 2.9 V to about 3.1 V. However, the disclosure is not so limited and the applied voltage may be different than that described above. In some embodiments, a voltage between the working electrode 166 and the reference electrode 170 is within a range from about 1.8 V to about 1.9 V. An electric potential may be applied between the counter electrode 168 and the working electrode 166, providing a polarization field and a driving force for moving the oxide ions dissolved from the metal oxide precursor at the working electrode 166 to the counter electrode 168, facilitating reduction of the metal oxide at the working electrode 166.

In some embodiments, the voltage applied between the working electrode 166 and the counter electrode 168 may be substantially constant. In other embodiments, a current between the working electrode 166 and the counter electrode 168 may be maintained as a substantially constant current.

Responsive to exposure to the applied voltage in the electrochemical cell 160, the metal oxide precursor 174 may be reduced to a substantially pure metal comprising the metal of the metal oxide precursor. The metal atoms may be reduced at the working electrode 166 to generate a substantially non-oxidized metal. For example, the reaction (1) below may occur at the working electrode 166:

MO_(x)+2xe ⁻→M+xO²⁻  (1),

where M is the metal of the metal oxide precursor and x is the amount of oxygen present in the metal oxide precursor. The electrons are provided in the electrochemical cell 160 by application of current to the working electrode 166.

Oxygen atoms from the metal oxide precursor 174 may be dissolved into the molten salt electrolyte 164 at the working electrode 166 and transported from the working electrode 166 to the counter electrode 168 responsive to exposure to the applied electrical field (i.e., a polarization between the counter electrode 168 and the working electrode 166. Oxide ions (O²⁻) may evolve at the counter electrode 168 according to the reaction (2) below:

2O²⁻→O₂+4e ⁻  (2).

The metal oxide precursor 174 may be exposed to the reducing conditions in the electrochemical cell 160 for a duration within a range of from about 1 hour to about 48 hours, such as from about 1 hour to about 6 hours, from about 6 hours to about 12 hours, from about 12 hours to about 18 hours, from about 18 hours to about 24 hours, from about 24 hours to about 36 hours, or from about 36 hours to about 48 hours. After a sufficient duration of time, the metal oxide precursor 174 may be substantially chemically reduced in the electrochemical cell 160 to form the reduced metal of the metal oxide precursor, which is substantially free of oxygen.

The insulating metal oxide (e.g., the metal oxide precursor, the first metal) is directly (electrochemically) reduced to its metallic constituent(s), while remaining in intimate contact with a metallic current collector (e.g., the second metal, a wire, a cathodic current collector), in a suitable electrolyte. By way of example only, a titanium-tantalum alloy may be directly formed from tantalum oxide by methods according to embodiments of the disclosure. The metallic current collector may function as a source of electrons in order to ionize oxygen to oxide ions (O²⁻). The metallic current collector may react (e.g., chemically react) with the reduced metal (at the cathode) to prepare the alloy in situ. Under the polarization conditions, the oxide ions enter the electrolyte and get discharged at the anode surface. The oxide ions leave the electrolyte and the cathode is converted to a porous metal or porous metal alloy. Gradual removal of oxygen from the metal oxide transforms the metal oxide into a reduced (porous) metal. The process utilizes the current collector to produce high temperature metal alloys without generating metal waste from the current collector. Unlike conventional methods, the current collector in the method according to embodiments of the disclosure is not degraded after prolonged exposure to corrosive molten salt media at elevated temperatures. In conventional methods, the degraded current collector becomes degraded and must be disposed of. Chemical reactivity or electrochemical reactivity between the reduced metal and the metal of the current collector is used to fabricate the alloy/alloy coating in situ. Therefore, the metallic current collector functions as a lead to form the alloy in situ. In contrast, conventional metallic current collectors are inert and do not take part in the alloy formation process.

The metal alloy may include, but is not limited to, Ta—Ti, Ta—Mo, Ta—Hf, or Ta—W. In some embodiments, the metal alloy is a Ta—Ti alloy. In other embodiments, the metal alloy is a Ta—Mo alloy. In yet other embodiments, the metal alloy is a Ta—Hf alloy. In still yet other embodiments, the metal alloy is a Ta—W alloy. The metal alloy may include the first metal at from about 10% by weight (wt. %) to about 90 wt. % and the second metal at from about 90% by weight wt. % to about 10 wt. %. The metal alloy may include from about 20 wt. % to about 60 wt. % of the first metal and from about 80 wt. % to about 40 wt. % of the second metal. By way of example only, the metal alloy may be a 80 wt. % Ta-20 wt. % Ti alloy, a 60 wt. % Ta-40 wt. % Ti alloy, or a 40 wt. % Ta-60 wt. % Ti alloy. A composition of the metal alloy may be tailored by adjusting process parameters of the polarization, such as one or more of the electrolyte composition, metal oxide composition, metal oxide morphology, polarization time, conditions of the polarization, applied current, etc.

The metal oxide precursor may, optionally, be formed into a desired shape by an additive manufacturing (AM) process. Then, the methods according to embodiments of the disclosure may be conducted as described above to form the metal alloy from the metal oxide precursor in a net shape component or a near net shape component, eliminating sintering, pressure bonding, injection molding, casting, extruding, or calendaring acts that are necessary in conventional processes of forming such components. Therefore, the methods according to embodiments of the disclosure may be used to form components as a net shape or a near net shape in a single act, reducing the number of process acts used to produce the components.

In some embodiments, an interlayer may, optionally, be formed between a base material (e.g., the substrate, the wire) and the tantalum alloy coating during the polarization in the electrochemical cell 160. The base material may be a metallic material or a non-metallic material. The base material may have a simple geometry or a complex geometry, and the presence of the interlayer may enable the tantalum alloy coating to be formed on and strongly adhered to the base material. The interlayer (e.g., a diffused interlayer) may be formed between the base material and the tantalum alloy coating. Without being bound by any theory, the interlayer may be formed by diffusion of the reduced metal from the surface. The metal oxide precursor is formed on the base material, such as by a coating process. The coated base material is subjected to the polarization conditions in the electrochemical cell 160 using, for example, a CaCl₂)/CaO electrolyte. The polarization process may be conducted at a temperature of from about 850° C. to about 900° C. for a duration ranging from about 5 hours to about 10 hours to form the interlayer and the tantalum alloy on the base material. The metal of the metal oxide precursor reacts with base material, forming inseparable bonds between the metal and the base material. After the polarization, the coated base material is annealed, such as at a temperature of about 600° C. The interlayer may improve the robustness of the tantalum alloy coating and prevent corrosion or other damage to the base metal. The interlayer may exhibit strong adhesion to the base material. In contrast to conventional processes, which form the metal alloy on the substrate, three distinct layers (the base material, the diffused interlayer, and the tantalum alloy coating) are formed by the methods according to embodiments of the disclosure. The diffused interlayer may be formed at a thickness sufficient to substantially cover the substrate. The thickness of the diffused interlayer may be further increased by annealing the article containing the diffused interlayer and the tantalum alloy layer. The diffused interlayer enables the tantalum alloy to adhere strongly to the substrate. The diffused interlayer also improves the durability of the resulting article, and enables the article to be subjected to bending, flexing and deformation without substantial chipping, spalling, or delamination.

In additional embodiments, a method of forming metal alloys or metal compounds is used to form a coating on a metal substrate or as a bulk alloy. The metal may be a transition metal or a refractory metal and the metal alloy or the metal compound may be a binary transition metal or a binary refractory metal alloy. In some embodiments, the metal is a transition metal. The metal alloy is formed from a metal oxide precursor or a mixed metal oxide precursor as described above. The metal alloy may be used as a metal coating on the metal substrate or as a bulk alloy. The coating of the metal alloy may be prepared by reacting in situ the metal of the metal oxide precursor with a metal or other element of the substrate. The metal oxide is reduced (e.g., chemically reduced) to the metal, which alloys with the metal of the substrate. The chemical reactivity or electrochemical reactivity of the reduced metal with the metal of the substrate produces the metal alloy. Alternatively, the coating of the metal alloy may be prepared by applying a mixed metal oxide coating to the substrate and co-reducing the oxides to form the metal alloy on the substrate.

The substrate may be a metal substrate, such as a tantalum substrate, a nickel substrate, a chromium substrate, a tungsten substrate, a titanium substrate, a stainless steel substrate, a copper substrate, or a molybdenum substrate. To form the coating on the substrate, a metal oxide material, such as hafnium oxide, may be formed on the substrate. The metal oxide material may then be reduced (e.g., chemically reduced) to form a metal coating (e.g., a metal layer) on the substrate. The chemical reduction of the metal oxide material may be conducted in the electrochemical cell 160 as described above using, for example, a CaCl₂)/CaO electrolyte. The metal of the metal oxide material may react with the metal of the substrate to produce the metal alloy in situ on the substrate. The coating to be formed on the substrate may, for example, be a tantalum-hafnium alloy. Alternatively, a mixed metal oxide material may be formed on the substrate and the metal oxide reduced (e.g., chemically reduced) to form a mixed metal coating on the substrate.

In some embodiments, the metal alloy is a tantalum-hafnium alloy. The tantalum-hafnium alloy is formed by forming a hafnium oxide coating on a tantalum substrate or forming a tantalum oxide coating on a hafnium substrate. After forming the oxide coating, the metal of the oxide coating is reduced (e.g., chemically reduced) to form a metal coating, which reacts with the metal of the substrate to form the tantalum-hafnium alloy. The metal of the oxide coating and the metal of the substrate are co-reduced to form the tantalum-hafnium alloy. The metal of the oxide coating is chemically reduced in an electrochemical cell 160 using a CaCl₂)/CaO electrolyte as described above. The metal coating may be adherent to the wire and be substantially pore free

To form the tantalum-hafnium alloy as a bulk alloy, sintered pellets of tantalum oxide (e.g., Ta₂O₅) and hafnium oxide (e.g., HfO₂) may be chemically reduced in an electrochemical cell 160 using a CaCl₂)/CaO electrolyte as described above.

The tantalum-hafnium alloy may be used in high temperature applications, such as at a temperature between about 1600° C. and 2200° C. or at a temperature greater than about 2000° C. The tantalum-hafnium alloy may also be used in oxidizing environments. By way of example only, the tantalum-hafnium alloy may be used in rocket thrust chambers and nozzles, re-entry vehicle leading edges, or ramjet engine structures.

In additional embodiments, a method of forming a metal alloy is used to prevent hydrogen embrittlement. Hydrogen embrittlement may occur in metals that form hydrides, which causes the metals to lose ductility. The hydrogen embrittlement occurs in metals that absorb hydrogen. The metal alloy may include, but are not limited to, tantalum-molybdenum, tantalum-tungsten, and tantalum-rhenium. The tantalum-molybdenum alloy, the tantalum-tungsten alloy, or the tantalum-rhenium alloy may be used in the corrosion industry, the aerospace industry, or the automotive industry. The presence of a small amount (e.g., from about 0.5 wt. % to about 1.5 wt. %) of the molybdenum, tungsten, or rhenium in the tantalum alloy prevents hydrogen embrittlement of the tantalum when exposed to concentrated acids, such as sulfuric acid, hydrochloric acid, nitric acid, or phosphoric acid. The metal alloy may be formed as a coating or a bulk material. The presence of the molybdenum, tungsten, or rhenium in the tantalum alloy may also prevent corrosion of the tantalum. A surface coating of a metal oxide on, for example, tantalum or molybdenum was formed by coating the tantalum or molybdenum with the metal oxide and reducing the metal oxide to the metal, which, in turn, is alloyed with the tantalum or molybdenum to form the alloy coating in situ. As described above, the chemical reduction may be conducted in an electrochemical cell 160 using a CaCl₂)/CaO electrolyte.

To form the alloy coating (e.g., a surface coating) of molybdenum, tungsten, or rhenium on tantalum (e.g., a tantalum wire), the tantalum may be coated with the metal oxide (e.g., the metal oxide precursor), which is reduced (e.g., chemically reduced) to the metal. For instance, molybdenum oxide or tungsten oxide (WO₂, WO₃, WO_(2.9), WO_(2.72)) may be coated on the tantalum and then reduced to molybdenum or tungsten, respectively, as previous described. The molybdenum or tungsten may react with the tantalum to form in situ the tantalum-molybdenum alloy or tantalum-tungsten alloy, respectively. Similarly, tantalum oxide may be coated on tungsten by forming a coating of the tantalum oxide on a tungsten wire and reducing the tantalum oxide to tantalum. The tantalum may react with the tungsten of the wire to form the tantalum-tungsten alloy.

Forming the tantalum-molybdenum alloy or the tantalum-tungsten alloy as a bulk material may be conducted by chemical co-reduction of a mixed metal oxide. The metals of the mixed metal oxide may be co-reduced and reacted with tantalum to form the tantalum-molybdenum alloy or the tantalum-tungsten alloy. To form the tantalum-molybdenum alloy, co-reduction of mixed metal oxides including Ta₂O₅ and MoO₂ may occur. Similarly, to form the tantalum-tungsten alloy, co-reduction of mixed metal oxides including Ta₂O₅ and WO₃ may occur.

The following examples serve to explain embodiments of the disclosure in more detail. These examples are not to be construed as being exhaustive or exclusive as to the scope of this disclosure.

EXAMPLES Example 1: Ta—Ti Alloy

High purity (99.9% pure) sintered tantalum oxide (Ta₂O₅) pellets were prepared by a powder metallurgical process. The green pellets were sintered both in air or under a reducing atmosphere (Ar—H₂ mixture/pure H₂ flow). The evaluation and characterization of the sintered pellets were carried out by powder XRD, SEM-EDS and porosity measurements. The sintered Ta₂O₅ pellets were then threaded into a 3 mm diameter titanium wire, which functioned as the current collector. The assembly was immersed in a CaCl₂)-1 wt. % CaO electrolyte and polarized against an iridium/ruthenium anode at 2.5-3.2 V (cell voltage) in the temperature range of from about 850° C. to about 950° C. for a duration up to about 24 hours to produce a coating of a Ta—Ti alloy. The Ta—Ti alloy included a 80 wt. % Ta-20 wt. % Ti alloy, a 60 wt. % Ta-40 wt. % Ti alloy, or a 40 wt. % Ta-60 wt. % Ti alloy. The polarization experiments were performed in a custom-fabricated argon atmosphere controlled glove box. The furnace was then switched off, the cathode assembly was removed from the electrochemical cell and the products were analyzed by XRD and SEM-EDS. Therefore, the titanium current collector was used to form a Ta—Ti alloy coating on the titanium wire from the metal oxide (Ta₂O₅) pellets.

Example 2, Ta—Ti Alloy

High purity (99.9% pure) sintered tantalum oxide (Ta₂O₅) and titanium dioxide (TiO₂) pellets were prepared by a powder metallurgical process. The green pellets were sintered in air or a reducing atmosphere (Ar—H₂ mixture). The evaluation and characterization of the sintered pellets were carried out by powder XRD, SEM-EDS and porosity measurements. The sintered Ta₂O₅ pellets were then threaded into a 3 mm diameter nickel wire (e.g., current collector). The assembly was immersed in a CaCl₂)-1 wt. % CaO electrolyte and polarized against an iridium/ruthenium anode at 2.5-3.2 V (cell voltage) in the temperature range of from about 850° C. to about 950° C. for a duration up to about 24 hours to produce a Ta—Ti alloy. The Ta—Ti alloy included a 80 wt. % Ta-20 wt. % Ti alloy, a 60 wt. % Ta-40 wt. % Ti alloy, or a 40 wt. % Ta-60 wt. % Ti alloy. The polarization experiments were performed in a custom-fabricated argon atmosphere controlled glove box. The furnace was then switched off, the cathode assembly was removed from the electrochemical cell and the products were analyzed by XRD and SEM-EDS. Therefore, the nickel current collector was used to form a bulk Ta—Ti alloy from the metal oxide (Ta₂O₅) pellets.

Example 3: Ta₂O₅/TiO₂ Pellets

The ball-milled powder was pelletized and sintered in a reducing atmosphere (under continuous dry hydrogen flow) at about 975° C. for about 1 hour. The color of the sintered pellet looked greyish-black. Such a pellet was observed to undergo complete reduction (to the alloy powder) at a duration of less than about 30 hours, such as about 20 hours. The reduced alloy powder was observed to contain relatively less residual oxygen content (about 50% less than the oxygen values obtained for the air-sintered pellet). Thus, the preparation of the metal oxide precursor in a reducing atmosphere prior to the electrochemical polarization was observed to offer significant benefits. The resulting Ta₂O₅/TiO₂ pellets are shown in FIG. 2, with the air-sintered pellet on the left side of the photograph and the sintered in a reducing atmosphere pellet on the right side of the photograph.

Example 4: Ta—Ti Alloy

Calculated quantities of high purity TiO₂ and Ta₂O₅ powders (1-20 micron range, total powder quantities: up to 10 g) were mixed with additives (polyethyl glycol and polyvinyl alcohol). The blended powder was added to 100 ml of isopropyl alcohol. The slurry was ball-milled for about 15 hours in an alumina ball milling device. The milled powder was compacted to pellets (about 1.5 mm diameter and about 2-3 mm thick) under a hydraulic pressing unit. The pellets were sintered in air at a temperature from about 950° C. to about 1000° C. for from 1 to 2 hours. The sintered pellets looked sturdy. A hole at the center of the sintered pellet was drilled to hang the pellet in the molten salt bath and to cathodically polarize the same against an inert anode (ruthenium and iridium rod). The polarization experiments were carried out (by controlling the cell potential in the range 2.5-3.1V) for durations up to about 36 hours. The reduced pellets were cleaned in water, ethyl alcohol and acetone successively to remove the adhered salt from the surface of the reduced pellets and the salt trapped inside the reduced (porous) pellet. The pellet crumbled to fine powders. The cleaned powders were evaluated and characterized by a suite of analytical tools (x-ray diffraction, scanning electron microscopy and residual oxygen measurement). These techniques indicated the formation of a fine Ta—Ti alloy powder, as shown in FIG. 3, having a particle size of from about 10 micron to about 20 micron.

Example 5: Ta—Ti Alloy

A 2 mm diameter and 100 mm long tantalum wire/rod was cleaned, first by a fine grade emery paper and then by electrochemical etching. A finely dispersed TiO₂ paste (prepared by mixing TiO₂ with isopropyl alcohol) was slurry-coated on about one-third of the length of the tantalum wire/rod. The coated rod was oven-dried at about 70° C. to 80° C. for about 12 hours. The dried rod was cathodically polarized against an inert anode for about 10 hours. The specimen was then taken out of the electrochemical cell and immersed in water to dissolve the adhered salt. The specimen was then subjected to ultrasonic cleaning and dried in an oven for about 20 hours at 90° C. in an oven, placed inside the argon atmosphere glove box. The heat-treated surface, upon examination under a scanning electron microscope, revealed two things: (1) the surface TiO₂ layer was converted to a porous titanium layer (˜0.5 mm thick) and (2) the surface titanium, during heat-treatment), diffused from to the bulk and alloyed with a portion of the tantalum rod (about 1 mm from the surface) to form the titanium-tantalum solid solution alloy film. The alloy film was observed not to have any intermetallic phase(s).

Example 6: Ta—Ti Alloy

A 1.5 mm diameter and 100 mm long titanium wire was coated with Ta₂O₅ powder (slurry coated). The oven-dried Ta₂O₅-coated wire was cathodically polarized against a ruthenium rod for 8 hours at 2.9 V (cell voltage). The wire, after polarization, was observed (under a scanning electron microscope) to have formed a porous titanium-tantalum thin surface layer/film (about 0.8 mm thick). Subsequent annealing at 100° C. for 5 hours in argon atmosphere was observed to be effective in eliminating the film porosity.

Example 7: Ta—Hf Alloy

High purity and finely powdered (˜10 micron) Ta₂O₅ and HfO₂ were mixed, ball-milled and compacted into pellets using a laboratory hydraulic pressing unit. The green pellets were sintered in air or a reducing atmosphere (under a continuous gas flow consisting of either a mixture of Ar—H₂ or pure H₂). In FIG. 4, the state of the sintered pellets prior to subsequent electrochemical polarization is shown, with the air-sintered pellet on the left side of the photograph and the sintered in a reducing atmosphere pellet on the right side of the photograph. The evaluation and characterization of the sintered pellets were carried out by powder XRD, SEM-EDS and porosity measurements. The HfO₂ pellets were then threaded into a tantalum wire. The assembly was immersed in a CaCl₂)-1 wt. % CaO electrolyte and polarized against an iridium/ruthenium anode at 2.5-3.2 V (cell voltage) in the temperature range of from about 850° C. to about 950° C. for a duration up to about 24 hours to produce a coating of a Ta—Hf alloy on the tantalum wire. The polarization experiments were performed in a custom-fabricated argon atmosphere controlled glove box. The furnace was then switched off, the cathode assembly was removed from the electrochemical cell and the products were analyzed by XRD and SEM-EDS.

Example 8: Ta—Hf Alloy

The sintered pellets were threaded to a nickel/Inconel 700/molybdenum wire and polarized against an anode (ruthenium/iridium/graphite rod) between 2.8-3.1V (cell voltage) for durations up to 48 hours at 950° C. The reduced pellets were removed from the cell and washed with water, ethyl alcohol and acetone. The cleaned powder was oven-dried at 90° C. for 10 hours in argon atmosphere. The powder was subsequently analyzed to have a composition of metallic tantalum and hafnium with traces of oxygen (<1%) as an impurity.

Example 9: Ta—Hf Alloy

The polarization of pellets, prepared in a reducing atmosphere, was observed to undergo faster transformation (to alloy phase) with relatively lesser amounts of residual oxygen contents (<0.5%). Like in the case of Ta—Ti alloys, such a behavior was also observed during the formation of the Ta—Hf alloy.

Example 10: Ta—Hf Alloy

A 1.5 mm diameter and 100 mm long tantalum wire was coated with HfO₂, heat-treated and polarized against an inert anode (iridium/ruthenium rod) at a cell voltage of 3.1V for 30 hours at 950° C. The tantalum wire, after polarization, was observed to have a porous and thin (˜0.3 mm thick) hafnium layer on its surface. Subsequent annealing in argon at about 90° C. for 5 hours were observed to be the sufficient conditions for (1) removing the surface porosity and (2) promoting the in situ (Ta—Hf) alloy formation by way of diffusion of Hf from the surface to the inner tantalum wire.

Example 11: Ta—Hf Alloy

A 1 mm diameter and 100 mm long Ta₂O₅-coated Hf wire was polarized at 950° C. for a duration of 8 hours at a cell voltage of 2.9V. The coated wire was observed to have formed a thin layer (˜0.3 mm) of Ta—Hf alloy.

Example 12: Ta—Hf Alloy

A 1.5 mm diameter and 100 mm long Mo wire was coated with a 1:1 mixture of Ta₂O₅ and HfO₂. The Mo wire was heat-treated and polarized for a duration of 20 hours at a cell voltage of 3.0V for 8 hours. The results indicated the formation of an Hf—Ta thin and porous film (˜0.2 mm thick) on Mo wire. Subsequent annealing in argon not only helped increase the alloy thickness but also removed the porosity.

Example 13: Ta—Hf Alloy

Tantalum oxide (Ta₂O₅) pellets and hafnium oxide (HfO₂) pellets were prepared in a manner similar to that described in Example 7. The green pellets were sintered in air or under a reducing atmosphere (Ar—H₂ mixture). The evaluation and characterization of the sintered pellets were carried out by powder XRD, SEM-EDS and porosity measurements. The Ta₂O₅ and HfO₂ pellets were then threaded into a molybdenum wire. The assembly was immersed in a CaCl₂)-1 wt. % CaO electrolyte and polarized against an iridium/ruthenium anode at 2.5-3.2 V (cell voltage) in the temperature range of from about 850° C. to about 950° C. for a duration up to about 24 hours to produce a coating of a Ta—Hf alloy on the molybdenum wire. The polarization experiments were performed in a custom-fabricated argon atmosphere controlled glove box. The furnace was then switched off, the cathode assembly was removed from the electrochemical cell and the products were analyzed by XRD and SEM-EDS.

Example 14: Ta—Hf Alloy

Tantalum oxide (Ta₂O₅) pellets and hafnium oxide (HfO₂) pellets were prepared in a manner similar to that described in Example 7. The green pellets were sintered in air or under a reducing atmosphere (Ar—H₂ mixture). The evaluation and characterization of the sintered pellets were carried out by powder XRD, SEM-EDS and porosity measurements. The assembly was immersed in a CaCl₂)-1 wt. % CaO electrolyte and polarized against an iridium/ruthenium anode at 2.5-3.2 V (cell voltage) in the temperature range of from about 850° C. to about 950° C. for a duration up to about 24 hours to produce a bulk Ta—Hf alloy. The polarization experiments were performed in a custom-fabricated argon atmosphere controlled glove box. The furnace was then switched off, the cathode assembly was removed from the electrochemical cell and the products were analyzed by XRD and SEM-EDS.

Example 15: Ta—Mo Alloy

A Ta—Mo alloy coating was formed on a tantalum wire (1 mm diameter). Upon annealing (inside the argon atmosphere glove box), a smooth, adherent and pore-free coating was formed. In this process, the tantalum wire was coated with molybdenum oxide (MoO₂). The wire was dried at a temperature less than 100° C. The coated wire was then cathodically polarized in the fused CaCl₂)-2-5 wt. % CaO electrolyte, for a duration of about 15 hours at 850° C. Upon removal of the wire from the electrochemical cell, it was observed that the surface MoO₂ was transformed to Mo, which, in turn, chemically reacted (through a surface diffusion phenomenon) to form the alloy coating in situ.

Example 16: Ta—Mo Alloy

Cathodic polarization of a mixed oxide (Ta₂O₅ and MoO₂) coating was conducted on a molybdenum wire, under similar conditions to those in Example 15, which resulted in the formation of a thin Ta—Mo alloy film on the molybdenum surface. A sintered pellet containing Ta₂O₅ and MoO₂ was threaded into a nickel wire and the cathode assembly was lowered into the molten CaCl₂)/CaO electrolyte. Following polarization in the molten CaCl₂)/CaO electrolyte for a duration of 20 hours at 850° C., resulted in the formation of the reduced (binary) Ta—Mo alloy.

Example 17: Ta—W Alloy

An in situ prepared alloy including a Ta—W coating on a tungsten wire (1 mm diameter) was prepared under similar conditions to those in Example 15. Upon annealing inside the argon atmosphere glove box, a smooth, adherent and pore-free Ta—W coating was formed. In this process, the tungsten wire was coated with WO₂ and placed in the electrochemical cell. The wire was dried at a temperature less than 100° C. The coated wire was then cathodically polarized in the fused CaCl₂)-3 wt. % CaO melt in the electrochemical cell for a duration of about 12 hours at 850° C. The reduction was conducted at a constant voltage for durations up to 20 hours. Upon removal of the wire from the electrochemical cell, it was observed that the surface WO₂ was transformed to tungsten, which, in turn, chemically reacted (through a surface diffusion phenomenon) to form the Ta—W alloy coating in situ (FIG. 5).

Example 18: Ta—W Alloy

Sintered pellets containing Ta₂O₅ and a tungsten oxide (e.g., WO₂ or WO₃) were threaded into a nickel wire and the cathode assembly was lowered into the molten electrolyte. The green pellets (13 mm diameter and 2-3 mm thick), as shown in FIG. 6, were sintered in air or in a reducing atmosphere (flowing hydrogen atmosphere). The temperature and heating duration of the sintering were in the range of from 800° C. to 1000° C. and from 1 hour to 3 hours respectively. Its polarization, in the CaCl₂)-3 wt. % CaO, melt for a duration of 20 hours at 850° C., resulted in the formation of the reduced Ta—W alloy.

Example 19

Stainless steel and copper substrates were coated with high purity tantalum pentoxide (Ta₂O₅). The coated substrates were then cathodically polarized in an anhydrous calcium chloride melt at a temperature between 850 and 900° C. for a duration ranging from 5 hours to 10 hours. A platinum group monolithic metal rod and glassy carbon rod were used as the counter (anode) and pseudo reference electrodes respectively. Upon polarization, the Ta₂O₅ progressively started losing oxygen. After the polarization, the coated substrates were annealed up to a temperature of 600° C. The annealed specimens were observed to form the diffused tantalum interlayer, as shown in FIG. 7.

While the disclosure is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. However, the disclosure is not limited to the particular forms disclosed. Rather, the disclosure is to cover all modifications, equivalents, and alternatives falling within the scope of the following appended claims and their legal equivalent. For example, elements and features disclosed in relation to one embodiment may be combined with elements and features disclosed in relation to other embodiments of the disclosure. 

What is claimed is:
 1. A method of forming a metal alloy, comprising: forming a metal oxide precursor on a substrate; and conducting cathodic polarization of the metal oxide precursor in a molten salt electrolyte to form a metal alloy on the substrate.
 2. The method of claim 1, wherein conducting cathodic polarization of the metal oxide precursor comprises conducting cathodic polarization to form a tantalum alloy on the substrate.
 3. The method of claim 1, wherein conducting cathodic polarization of the metal oxide precursor comprises conducting cathodic polarization to form a tantalum-transition metal alloy or a tantalum-refractory metal alloy on the substrate.
 4. The method of claim 1, wherein conducting cathodic polarization of the metal oxide precursor comprises conducting cathodic polarization to form a tantalum-tungsten alloy, a tantalum-titanium, a tantalum-hafnium alloy, or a tantalum-molybdenum alloy on the substrate.
 5. The method of claim 1, wherein conducting cathodic polarization of the metal oxide precursor comprises forming the metal alloy on a metallic substrate.
 6. The method of claim 1, wherein conducting cathodic polarization of the metal oxide precursor comprises forming the metal alloy on a non-metallic substrate.
 7. A method of forming a metal alloy, comprising: forming a metal oxide precursor; reducing the metal oxide precursor to a metal in an electrochemical cell, the electrochemical cell comprising a working electrode, a counter electrode, and an electrolyte; and reacting the metal of the metal oxide precursor with a metal of the working electrode to form a metal alloy.
 8. The method of claim 7, wherein forming a metal oxide precursor comprises forming the metal oxide precursor by an air sintering process.
 9. The method of claim 7, wherein forming a metal oxide precursor comprises forming the metal oxide precursor under a reducing atmosphere.
 10. The method of claim 7, wherein forming a metal oxide precursor comprises forming the metal oxide precursor comprising one or more metal oxide materials.
 11. The method of claim 7, wherein reducing the metal oxide precursor to a metal in an electrochemical cell comprises reducing the metal oxide precursor to the metal in the electrochemical cell comprising a molten salt electrolyte.
 12. The method of claim 7, wherein reducing the metal oxide precursor to a metal in an electrochemical cell comprises reducing the metal oxide precursor to the metal in the electrochemical cell comprising a molten electrolyte comprising calcium chloride and calcium oxide.
 13. A method of forming a metal alloy, comprising: forming a metal oxide precursor on a base material; introducing the base material into a molten salt electrolyte of an electrochemical cell; reducing the metal oxide precursor to a metal in the electrochemical cell; and reacting the metal of the metal oxide precursor with the base material to form a metal alloy on the base material.
 14. The method of claim 13, wherein forming a metal oxide precursor comprises forming the metal oxide precursor comprising a unitary metal oxide, a binary metal oxide, or a ternary metal oxide.
 15. The method of claim 13, wherein introducing the base material into a molten salt electrolyte of an electrochemical cell comprises at least partially disposing the metal oxide precursor and the base material into the molten salt electrolyte.
 16. The method of claim 13, wherein reducing the metal oxide precursor to a metal comprises electrochemically reducing the metal oxide precursor to the metal in the electrochemical cell.
 17. The method of claim 13, wherein reacting the metal of the metal oxide precursor with the base material comprises forming the metal alloy and an interlayer on the base material.
 18. The method of claim 17, wherein forming the metal alloy and an interlayer on the base material comprises forming the metal alloy and a diffused metal interlayer on the base material.
 19. The method of claim 18, wherein forming the metal alloy and a diffused metal interlayer on the base material comprises forming a tantalum alloy and a diffused tantalum layer on the base material.
 20. The method of claim 13, wherein forming a metal oxide precursor occurs before reducing the metal oxide precursor to a metal and reacting the metal of the metal oxide precursor with the base material. 